European On-Board Diagnostics, Basic Function - GF07.10-P-1057A
Engine all (4xWD)
Engine all (CAR)
Overview
This document contains information on:
- General
- Function requirements
- Function
- European On-Board Diagnosis
- Fault detection
- Fault testing
- Components and system monitoring
- Performing readiness tests
- Fault storage
- Avoiding consequential faults
- Saving the fault freeze frame data
- Fault message
- Reading out the fault memory
- Deleting faults
General
European On-Board Diagnostics (EOBD) is a diagnostic system in the vehicle that monitors emissions-relevant systems and associated control units while driving. The objective is to determine and monitor malfunctions and exceeding of emission levels.
The EOBD stores malfunctions, communicates them to a diagnostic device via the diagnostics connection, and displays them in the instrument cluster through icons. As a result, the EOBD contributes to the reduction of exhaust gas emissions and protects vulnerable component parts from damage.
Function requirements
- Engine management ON (circuit 87M)
Function
European On-Board Diagnosis
Legislation requires electrical monitoring of components and systems with regard to their exhaust emission values and functionality as well as a plausibility test for sensors.
The EOBD monitors the emissions-relevant systems and components listed in the table for malfunctions.
| Diesel engines | Gasoline engines |
|---|---|
| Exhaust aftertreatment system | Lambda sensors upstream and downstream of the catalytic converter |
| Diesel particulate filter | Gasoline particulate filter |
| Glow system | Catalytic converter function |
| Intake air path | Catalytic converter heating |
| Fuel system | Purge control |
| Cooling system | Smooth engine running analysis |
| Crankcase ventilation system | Central gateway control unit |
| Smooth running control | Cooling system |
| Exhaust gas recirculation | Restraint systems control unit |
| Restraint systems control unit | Drivetrain control unit |
| Central gateway control unit | Rain/light sensor with additional functions |
| Drivetrain control unit | DC/DC converter control unit |
| Rain/light sensor with additional functions | Coolant temperature sensor |
| DC/DC converter control unit | - |
| Coolant temperature sensor | - |
All systems that, if faulty, would prevent the diagnosis of other systems are also included.
Fault detection
The combustion engine control unit checks the input and output signals for a permanent fault or signal interruption. The following faults are recognized according to their frequency and duration:
- Signals above or below the limit value
- Implausible signal combination
- Closed-loop control circuit above or below the limit of the regulation interval
- Faults in function chains
- Faults in the bus systems
Fault testing
Fault testing can relate to components or function chains. Component testing comprises the direct testing of a component part. In this case, the power supply and power circuits are monitored and sensor signals are compared.
For component parts and systems that cannot be tested with the aid of component testing, the function chain test is available. It involves indirect testing, with the combustion engine control unit actuating component parts and systems in a targeted manner and evaluating the resulting sensor signals.
Function chains check the systems listed in the table.
| Diesel engines | Gasoline engines |
|---|---|
| Smooth running control | Self-adjustment of mixture formation |
| Exhaust gas recirculation | Smooth running analysis (recognition of combustion misfires) |
| - | Catalytic converter function |
| - | Oxygen sensors (aging and controlling) |
| - | Oxygen sensor heater |
| - | Purge control |
Components and system monitoring
The monitoring of components and systems can take place cyclically or continuously. Components and systems that are not permanently active are monitored cyclically.
As a result, monitoring takes place only in defined operating phases. In the case of continuous monitoring, permanent monitoring takes place from the engine start to ignition OFF (circuit 15).
The following systems listed in the table are monitored.
| Monitoring type | Diesel engines | Gasoline engines |
|---|---|---|
| Cyclical | Fuel system | Catalytic converter function |
| Exhaust gas recirculation | Catalytic converter heating | |
| Smooth running control | Oxygen sensors (aging and controlling) | |
| Soot particulate filter regeneration | Oxygen sensor heater | |
| - | Purge control | |
| CONTINUOUS | Intake air path | Smooth engine running analysis |
| Glow system | Self-adjustment of mixture formation | |
| Soot particulate filter | Soot particulate filter regeneration | |
| Exhaust aftertreatment system | Automatic transmission | |
| Crankcase ventilation system | - | |
| Cooling system | - |
Performing readiness tests
With the readiness test, the EOBD performs a check as to whether diagnoses have taken place on non-permanently active systems (e.g. exhaust gas recirculation).
The readiness code is set for checking. It comprises two binary 12-digit series of numbers.
One of these series of numbers provides information on whether a specific component part or a specific function is being checked in this vehicle. 0 (component part not available or not in scope of testing) or 1 (component part available and in scope of testing) are assigned to the digits.
The second series shows the status of the tests that were carried out. In this case, each digit can be assigned 0 (diagnosis carried out) or 1 (diagnosis not carried out or canceled). The readiness code is set if the testing of all systems and components has taken place at least once per driving cycle.
Fault storage
The documentation of emissions-relevant faults takes place in the form of a fault code known as the Diagnostic Trouble Code (DTC). The EOBD stores the faults until the control unit confirms them. If the fault occurs in two consecutive driving cycles, the combustion engine control unit also stores it in the fault memory.
A driving cycle consists of an engine start, vehicle journey and stopping the engine, whereby an increase in coolant temperature by at least 22°C to at least 70°C must occur.
Avoiding consequential faults
Consequential faults occur if a faulty signal is detected and stored. To prevent consequential faults, all tests that have used a faulty signal as a benchmark are canceled.
Saving the fault freeze frame data
If a fault occurs twice, the operating conditions are also stored as fault freeze frame data. If the fault occurs more than twice, an update to the most recently stored fault freeze frame data takes place.
The fault freeze frame data includes:
- Vehicle speed
- Engine speed
- Temperature values (coolant, intake air, and charge air)
- Boost pressure
- Supply voltage
- Engine throttle condition
- Adaptation value for injection regulation
- Status of the lambda control
Fault message
A fault message is issued as soon as a fault occurs in two consecutive driving cycles. Then the engine diagnosis indicator lamp icon lights up in the instrument cluster.
In the event of misfires, the icon flashes and then lights up permanently during the whole remaining driving cycle. The fault message goes out after three consecutive driving cycles.
Reading out the fault memory
The fault memory of the combustion engine control unit can be read out via a diagnostic device or the XENTRY Diagnosis COM Kit. For this purpose, the ignition must be switched on or the engine must be running. Fault codes, fault freeze frame data, and readiness codes are stored in the fault memory.
Deleting faults
The fault memory of the combustion engine control unit deletes stored content after 40 consecutive driving cycles without a fault. The fault memory can be cleared after a repair or diagnostics with a diagnostic device or with the XENTRY Diagnosis COM Kit. When clearing the fault codes in the fault memory, all readiness codes are automatically reset.